The present invention is related to a solid electrolytic capacitor and a method of manufacturing a solid electrolytic capacitor. More specifically, the present invention is related to a method of forming a conductive bridge for improved formation of a cathode comprising an electrochemically polymerized intrinsically conducting polymer.
Solid electrolytic capacitors are well known in the art. Solid electrolytic capacitors comprising an intrinsically conductive polymeric cathode are also well known. A particular problem with solid electrolytic capacitors comprising an intrinsically conducting polymeric cathode is the cost of manufacturing, variation in polymer coverage and the buildup, or thickness, within each part and from part to part. Manufacturing cost is associated with two things. One is the repetitive number of dip/dry cycles required for chemical in-situ polymerization which is required to achieve sufficient coverage. The other is the cost and complexity of the equipment with the current methods of electrochemical polymerization.
Due to the highly resistive nature of the dielectric it is difficult to form the polymeric coating by passing current through the dielectric from the anode. To avoid this problem a conductive seed layer is typically formed on the dielectric then an external electrical contact is placed in contact with the conductive seed layer. This arrangement typically requires complex hardware or limits product design to those that allow for the external connection. The traditional external connection methods have a high potential for damage to the active surface of the element. This damage occurs in current manufacturing methods which require a direct physical contact between the external hardware and the conductive seed layer. The external hardware is incompatible with the dielectric and physical damage to the dielectric and/or polymeric cathode layer is common. Damage to the polymeric cathode layer may result in insufficient polymer coverage of the dielectric, that could lead to subsequent cathode layers damaging the dielectric properties, or subsequent processing damage of the exposed dielectric.
The present invention provides a very efficient method of forming a conductive polymeric coating whereby the external electrical contact is improved by the process of electrically separating the external electrical contact from the active cathode region of the element. This is accomplished without detrimental impact on the polymer quality, either physically or electrically, or the underlying dielectric and anode layers.